1. Field of the Invention
The present invention relates to an ink jet recording apparatus for performing recording by ejecting ink from the discharging ports to cause the ink to adhere to a recording material. More particularly, the invention relates to an ink jet recording apparatus provided with a recovery system including ink suction means to enable the recording head to maintain its stabilized ink ejection function, and such a recovery mechanism.
2. Related Background Art
Ink jet recording apparatuses are often provided with recovery means for recovering the ink ejection function of the recording head by removing the ink with increased viscosity and dust particles which adhere to the discharging ports of the recording head.
A recovery means of the kind comprises a cap to prevent ink from being dried in the discharging ports of a recording head; a pump unit to suck ink; and a wiping unit to wipe off the ink with increased viscosity, dust particles, and the like which adhere to the surface of the ink discharging ports. The driving force for those elements is transmitted from a carrier motor which drives a carriage.
In other words, for the ink jet recording apparatus, such a recovery means is not necessarily driven while the apparatus is engaged in its usual recording operation. Therefore, a clutch gear which engages with the pinion of the carrier motor is provided and then the clutch gear is shifted only when necessary to transmit the driving force to the recovery means therethrough. Thus, the number of motors is reduced.
Also, for the pump unit, a plunger type pump is mainly employed. A pump unit of the kind is of such a structure that only the piston which serves as a sealing member is reciprocated in the cylinder thereby to suck ink into the cylinder from the recording head with the negative pressure generated in the advancing stroke of the piston and exhaust the ink in the cylinder to an exhaust system in the returning stroke thereof.
In this type of conventional ink jet recording apparatus, it is necessary to provide a gear system including a clutch gear with a shaft, fixing wall, and other related components to support the gear system for the transmission of the driving force to its recovery means, which presents one of the hindrances to the miniaturization of the apparatus and the reduction of the manufacturing cost.
Also, with an additional arrangement of the gear, there are disadvantages in the aspects of the transmission efficiency and noises.
Also, in this type of conventional pump unit, there is a possibility that the ink which is supposed to be exhausted outside the cylinder by the returning stroke of the piston cannot withstand the liquid passage resistance in the exhaust system, and then the ink tends to be reversely forced into the recording head side from the ink suction inlet of the cylinder. Thus, if this reverse current phenomenon takes place, grease in the cylinder is carried to the discharging ports of the recording head to be mixed with ink before being ejected. There is a risk to create drawbacks such as an extreme degradation of the recording quality and the leakage of ink from the cap covering the recording head. Conventionally, therefore, a method is employed to provide a one-way valve for the ink passage in order to prevent the above-mentioned back flow of ink. However, with this method, there is a drawback that not only the cost is increased, but also the valving function of the one-way valve is hindered when ink is firmly fixed thereto. This cannot be an effective countermeasure.
Also, in a conventional cap of the kind, scratches tend to occur on the sealing surface when it is produced and also the defective caps can easily deformed due to insufficient filling of material. To increase its yield, therefore, the thickness of the sealing portion should be made thicker. Then, a problem is encountered that the deformation of the sealing surface is inhibited and then its sealing capability is lowered. Also, the silicone rubber which has an excellent ability to restore from compression over a wide temperature range can be formed by means of ejection molding. However, its gas transmissivity is so high that ink is easily evaporated when it is used as a cap. Thus, a problem is encountered that its anticipated effect to prevent ink from becoming too viscous is lowered.